The conventional switched reluctance motor has been around for well over a century. However, commercial viability and widespread utilization of the SRM has been hindered in recent decades for various reasons including poor control techniques, excessive audible noise, and large torque ripple. Despite these disadvantages, the SRM is of interest due its relatively simple construction and resulting lower cost when compared to other traditional electric motors. Because the traditional reluctance motor only has stator windings, the points of failure can only be the windings and shaft bearings. This provides for higher reliability. Additionally, with sufficient phase count the traditional SRM is able to function in the event of a phase failure as there is no flux linkage between phases to produce back-emf on the failed phase.
The traditional SRM topology, such as shown in FIGS. 17A and 17B, has changed little from its inception. Essentially, the conventional SRM consists of a stator 100 with salient teeth 102a-102b and current carrying windings (not shown) that are used to produce flux in a path that links through rotor teeth 104a-104b and a rotor yoke 106. The rotor yoke 106 and stator yoke 100 of the traditional SRM are additionally used for mechanical integrity and rigidity. The flux linkages generated between the stator and rotor of a traditional switched reluctance motor are designed to link primarily in plane(s) perpendicular to the axis 108 of shaft rotation and in the plane 110 of rotor rotation (i.e. radial gap motors). A similar process occurs for axial gap motors except that the flux linkages generated between the stator and rotor of the traditional SRM link primarily in paths parallel to the axis 108 of shaft rotation and perpendicular to the plane 110 of rotor rotation.
For example, as shown in FIGS. 17A and 17B, the primary flux path 103 of the traditional SRM is through the salient stator teeth 102a, salient rotor teeth 104a, the rotor yoke 106, an opposing salient rotor tooth 104b, an opposing salient stator tooth 102b, the stator yoke 100 and back through the originating stator tooth 102a. This flux path lies within a plane 110 that is perpendicular to the axis of shaft rotation.
A common variation to the reluctance motor design is the stacking of multiple reluctance motors, end to end, along a common shaft, at angular offsets so as to increase the magnitude of the generated torque and reduce torque ripple.
Numerous schemes for increasing the controllability of the traditional reluctance motor have been implemented. These schemes vary from innovative control algorithms to novel tooth designs. In one scheme described in U.S. Pat. No. 6,700,272, the motor runs at high speeds yet produces low shaft revolutions per minute (RPM). This allows for reduced torque ripple and results in a shaft RPM usable by most applications, thereby eliminating the need for a gearbox. This particular method has been accomplished through the introduction of differing flux guidance paths that result in a planetary gear effect between the rotor and stator. Despite this, the overall motor topology and planar torque production method is not different from that of the traditional SRM.
No known prior SRM design schemes have altered the fundamental design of the reluctance motor such that the path of the flux linkage through a rotor tooth is variable with position.